Save on bulk sheet filter fabric. This 18 x 36 inch sheet will provide 50 pcs of 90mm filter discs to fit Wide Mouth Mason jars, at a fraction of the cost. Easily cut with scissors for a custom fit. Polyethylene (PE) filter material is formed by a sintering process. This begins with a raw powder material of polyethylene particles, which are precisely graded to size by sieving. This powder is placed under controlled pressure and heat in large forming molds. As the particles bond the result is a durable, non-absorbent filtering mat, the pore size determined by the particle size, used. At .3 microns, these filter discs will exclude airborne bacteria but still allow air exchange, making them ideal for maintaining cultures free of bacterial contamination.